This invention relates generally to temporary storage receptacles and more particularly to a hopper for charging semiconductor source material in a Czochralski crystal pulling apparatus.
In operation of the Czochralski method of single crystal growth, a quantity of source material is formed in a crucible by melting solid semiconductor source material maintained in an inert environment at a vacuum pressure. As the crystal is grown, the source material is drawn off from the melt so that upon completion of the growth of one crystal, there is not enough semiconductor source material remaining in the crucible to grow a second crystal.
In the past, the provision of more source material from the second crystal was accomplished by shutting down the crystal pulling apparatus and bringing its interior to the room conditions. A new crucible with solid semiconductor source material in it was placed in the crystal pulling apparatus. The crystal pulling apparatus was then closed, the crucible environment was adjusted as needed for room conditions, and the source material was heated to form a new melt. This process was very time consuming, requiring many hours between successive crystal growths. In most cases, replacement of the melt as described required use of semiconductor source material in the more expensive form of blocks for melting.
One alternative to replacing the melt in the crystal pulling apparatus, is to replenish the melt (i.e., "batch recharge") by the addition of source material to the crucible, often in solid form, without shutting down the crystal pulling apparatus, Presently, temporary storage receptacles for semiconductor source material are located on the exterior of the crystal pulling apparatus and permanently attached to the crystal pulling apparatus. Semiconductor source material is delivered through a special opening in a wall of the crystal pulling apparatus. Expensive valving at the special opening is required to avoid loss of the environment and contamination of the melt when source material is added. Commercial producers of semiconductor material have been faced with undesirable choices if they wish to employ batch recharge so that more crystals may be grown before the crystal pulling apparatus must be shut down to replace the melt. They must either purchase a new crystal pulling apparatus having the permanently attached semiconductor source material storage receptacle, or accept radical and expensive modification of their existing crystal pulling apparatus.